The distribution of inhaled and intravenously injected radioactive xenon will be measured to determine respectively regional ventilation and regional blood flow in the lung. The matching in lung regions of local blood and gas flow will be studied in normal humans to determine how it is affected by aging, cigarette smoking, body position, exercise, hypoxia and high altitude acclimation. Patients with asthma, emphysema, valvular heart disease and other chronic cardiopulmonary disorders will be similarly studied to determine how regional lung function is altered in these diseases. The information gained from this research will give further understanding into mechanisms controlling small bronchi and blood vessels in the lungs and may also assist in the interpretation of cliniical lung scans.